1. Field of the Invention
The present invention relates to an optical recording medium in which information is recorded in the form of pits, a method of reproducing the information from this medium, and an optical information reproducing apparatus such as an optical disk apparatus and an optical card apparatus using this method.
2. Description of the Related Art
An optical disk reproducing apparatus is adapted to read and reproduce information recorded along tracks formed spirally or concentrically on a rotating optical disk upon irradiation by a laser beam thereof, and can be used as an information memory of very large capacity. The recorded information will have been recorded in the form of recesses called pits in correspondence with modulated signals which are normally digitally converted. Reproduction is effected by irradiating the disk with the laser beam and detecting a difference in the quantity of reflected or transmitted light which varies in accordance with the presence or absence of the pits. Such optical information recording media can be broadly classified into three different types: those used exclusively for reading, those which can be written on only once (referred to as the additional writing type), and those which can be overwritten.
The information which is generally recorded in the above-described optical information recording media includes, for instance, audio information or video information, or both. In any case, the information recorded on the disk employs one system of signal rows. For instance, U. S. Pat. No. 4,041,530 (issued on Aug. 9, 1977) discloses a recording medium which has pits with a depth of .lambda./4 with respect to the reproducing light having a wavelength .lambda.. Such a medium has naturally been subject to restrictions in the beam width and the like of recording signals owing to restrictions in the recording density, transfer rate, etc.
In addition, in order to increase the amount of information recorded on the optical recording medium, the intervals between the recording pits on the recording medium may be narrowed. As a practical matter, however, there arises the problem of information being mixed in from adjacent tracks (i.e., crosstalk) during reproduction, which disadvantageously limits the recording density.